Properties of RBCs and their influence on the quality of restoration 5 Flashcards
general notions about setting quality
Setting reaction. The quality of the polymerisation 55-75%
Chemical activation:
gradual increase of the viscosity
hard surface = complete polymerisation – first minutes limited working time (90 sec - 5 min.)
Self-curing (Autopolymerisation)
nitiated under the action of the initiator from the liquid
- under the chemical reaction of the N,N dimethyl p-toluidine, (activator), there are formed free radicals starting from benzoyl peroxide (initiator)
- the speed of polymerisation depends on the activator / initiator ratio
- exothermal reaction- it affects the dental pulp
- the setting time may be influenced by the:
- environmental T (directly proportional)
self-curing applications
RBC - indications
– fillings
– pits and fissures sealing
– core build-ups
– dental splints for teeth with periodontal diseases
– resin cements used for luting prosthetic restorations
adv and dsv od self curing
advantages which still assure its viability:
- it doesn’t need special equipment
- assures an uniform/homogeneous polymerisation, without depending on the thickness of the RBC layer
disadvantages which have influenced the appearance of the light- cured RBCs on the dental market: - chemical instable - air bubbles formation during mixing - questionablehomogenization - higher polymerisation shrinkage - toxicity of the monomer for the mucosa - continuous increase of the viscosity of the paste during working with working time limitation
Light-curing
is based on the organic matrix content in light- sensitive substances, excitable to different wavelengths (CQ – 470nm)
- in the past- were used lamps based on UV radiation ( 365nm – bad radiations, reduced penetration, without effects on the microfilled RBCs), later, it was used the light from the visible spectrum
light curing units According to the lightsource
- With incoherent radiation (visible spectrum)
- With coherent radiation (laser units) 3. With plasma generator
- With polarized light
light curing units according to aspect
optic cable based on glass fibers/ fluid conductors/ quartz/ plastic fibers/ pressed glass fibers
– With a wire cable between the source and the hand piece/ wireless
– Pencil system/ gun (compact transmission)
Types of light curing units
halogen lamps
light emitted diodes (=LED) lamps
laser lamps
plasma lamps
halogen lamps
they have colour filters which reduce the light intensity
– the longer the irradiation time is, the more increased the temperature will be
– an irradiation of 60 sec determines the increase of T • superficial with 4-15°C
•at 1 mm depth with 2-12°C
• at 2 mm depth with 1-7°C
light emitted diodes (=LED) lamps
without filter, “cold” light (questionable)
Light-curing units
halogen lamps
– they have colour filters which reduce the light intensity
– the longer the irradiation time is, the more increased the temperature will be
– an irradiation of 60 sec determines the increase of T • superficial with 4-15°C
•at 1 mm depth with 2-12°C
• at 2 mm depth with 1-7°C
– increased efficiency compared with the halogen lamps (reduced irradiation time)
– they aren’t compatible with any RBC –there are other light-sensitive substances with a different wavelength(for translucent or bleached shades):
=> licirin(400nm)
=> phenyl-propane-dione (430nm)
– they are lightweight and able to be charged with batteries
laser lamps
mechanical properties much more improved
– affected interface– quick polymerisation, of the whole block of material
–local T is much more increased (block polymerisation)
– there has to be a compatibility between the wavelength of the laser and the RBC
plasma lamps
there is a reduced light-curing time (2s/cycle)
– increase of the pulp T with only 2.2°C
– very expensive and incompatible between wavelengths of the
lamp and those of the light-initiator
dual cure systems used in the dental office
self- and light- cured
they initially appeared for the resin cements (combine the advantages of the both polymerisation types)
light curing adv and dmv
Light activation:
unlimited working time afterlightexposure- settingondemand
initialactivationwithinthesuperficiallayers(rateof 70%nearthe source)
in the first 10 sec takes place 60% from the polymerisation reaction, the rest of the material will be slowly cured (several hours – days)
the light intensity at the x distance from the material’s surface is:
Ix=Ioe-μx,
Io =intensity of the light at the surface
μ = is the coefficient of absorption of the material
polymerisation depth is limited ( the polymerisation rate decreases
rapidly with the thickness of the RBC)
the depth polymerisation depends on the
concetration of the CQ
the opacity degree of the material (max 2mm of the increment)
filler degree, type and size of the particles (reduced for the microfilled composites with many and small particles which are able to disperse the light)
intensity of the irradiation (radiometer)
compatibility between the light source and the composite material (there are variations of the light intensity until 10 times for the same wavelength - 470nm)
narrow spectrum – higher efficiency
proper exposure time required by the manufacturer distance from the light source
the way how the light-curing is done – passing or not through
other tissues
how to increase the during quality (for self curing)
self-curing
respect of the optimal dosage between the components (base and catalyst)
setting under pressure of a transparent celluloid matrix, otherwise it will result a rough layer due to the oxygen from the atmosphere which inhibits the polymerisation
how to increase the curing quality(for light curing)
minimum distance between the material and the lamp
interchangeable tips with small diameters (for the base cavity)
in rest, tips bigger than the dental cavity !!!! transparentmatricesfor lightre-direction
(gingival wall)
reduced thickness of the increments –less than 2mm when:
is used an opaque material (an opaque shade of the composite)
polymerisation through dental tissue
increase of the curing time to minimum 40 sec
Polymerisation shrinkage (0.9-1.5-3%) Depends on the :
% of filler (hybrid composites - minimum)
i resin type - Bis-GMA; UDMA (more reduced)
i quantity of the used material (dental cavity dimension) i filling technique and light-curing technique
how the type of base monomer is affecting the shrinkage???
methacrylate-during polymerization reaction of the rc based on methacrylate the molecules of the linear monomers approach to each other and they have a linear bonding.this thing has as a result a loss in volume of the cured material.
siloxane-during polymerization reaction of the rc based on siloxanes,takes place a reaction of the ‘‘cycle opening’’ in which the monomers bond to each others through opening flattening and stretching one towards the other.this behavior has as a result a reduced shrinkage.
how is light curing affecting shrinkage?
Direction of the polymerization shrinkage
Configuration factor (C-factor) = bonded surfaces/ unbounded surface Use of small increments(1-2 mm) instead of a bulk RBC when restoring a tooth cavity!!!!!
how to compensate polymerization shrinkage?
Can be compensated through:
slow expansion due to water sorption – gradually within several weeks after filling application
RBC use with a higher amount of inorganic filler
slow initiation of the light-curing
Direction techniques of the light source (towards the cervical margins or the lateral walls, through dental tissues)
Slow initiation of the light-curing – creates the possibility of the material‘s creep
happlication of the material using small increments (2mm) through zig-zag technique or through vertical application (to diminish of the C factor)
hliners/base application of a thicker layer
negative effects of polymerization shrinkage
1.stress over the dental tissues (residual cusps within class II cavities)
2. postoperative sensitivity/ cusp fracture
3. compromise of the marginal fit
(rupture of the adhesive bond of the tooth-filling complex)
4. secondary caries
